Well, kingship and priesthood are Jesus' because of who He is, not His boiology. So it's irrelevant.
As for "affiliation" I am not sure what you are saying. Someone who is adopted and stays with a tribe for his entire life is not a "part" of the tribe? He can never marry, or must find some other "misfit" to marry?
SD
Someone "adopted" into a different tribe (there was no legal adoption in biblical times) remained a member of the tribe in which they were born. Someone from the tribe of Judah did not gain the ability to serve as a priest simply because he was adopted into a Levite family.
Members of the different tribes could marry whomever they wished. There was no restriction on someone from Judah marrying someone from Benjamin. The children would be considered as being of the same tribe as the father. The only restriction was with the Levites, who were expected to marry within the tribe.
Its relevant because to fulfil the messianic prophecies, he had to be of the "seed of David" (and the author of the gospel of John agrees!).